Electrolyte for lithium secondary battery and lithium secondary battery including the same

ABSTRACT

An electrolyte for a lithium secondary battery and a lithium secondary battery including the same are provided. The electrolyte includes a non-aqueous organic solvent, lithium salt, and an additive that is either a dicarboxylic acid anhydride and a halogenated ethylene carbonate or a diglycolic acid anhydride and a halogenated ethylene carbonate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/505,953, filed on Aug. 18, 2006, entitled “ELECTROLYTE FOR LITHIUMSECONDARY BATTERY AND LITHIUM SECONDARY BATTERY INCLUDING THE SAME,”which claims priority to and the benefit of Korean Patent ApplicationNos. 10-2005-75685, filed on Aug. 18, 2005, and 10-2006-2439, filed onJan. 9, 2006 in the Korean Intellectual Property Office, the disclosuresof all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aspects of the present invention relate to an electrolyte for a lithiumsecondary battery and a lithium secondary battery including the same.More particularly, aspects of the present invention relate to anelectrolyte for a lithium secondary battery that has a long life andthat is preserved well and a lithium secondary battery including thesame.

2. Description of the Related Art

Recently, as apparatuses such as camcorders, mobile telephones, andnotebook personal computers (PC) become smaller and lighter and havehigher performances due to the rapid developments of electronicindustry, communication industry, and computer industry and electronicproducts, light and reliable batteries that can be used for a long timeare required. In particular, since a rechargeable lithium secondarybattery has an energy density per unit weight that is three times higherthan the energy densities per unit weight of a conventional leadbattery, a conventional Ni—Cd battery, a conventional Ni—H battery, anda conventional Ni—Zn battery and can be rapidly charged, research anddevelopment on the rechargeable lithium secondary battery has activelyperformed worldwide.

Lithium metal oxides are used as the positive electrode active materialsof a lithium secondary battery. A lithium metal, a lithium alloy,(crystalline or amorphous) carbon, and a carbon composite are used asthe negative electrode active materials of a lithium secondary battery.The term “lithium secondary battery” may refer to a lithium ion battery,a lithium ion polymer battery, or a lithium polymer battery inaccordance with the kind of separator and electrolyte that are used. Alithium secondary battery may be a cylinder type battery, a polygon typebattery, a coin type battery or other types in accordance with the shapethereof.

The average discharge voltage of the lithium secondary battery is in therange of from 3.6V to 3.7V, which is higher than the discharge voltagesof other alkali batteries such as a Ni-MH battery, or a Ni—Cd battery.However, in order to obtain such a high driving voltage, the electrolytecomposition used in the battery should be electrochemically stable inthe range of from 0V to 4.2V, which is the charge and discharge voltageregion. Therefore, an organic electrolyte obtained by dissolving lithiumsalt in a non-aqueous organic solvent is used as an electrolyte for alithium secondary battery. An organic solvent having high ionconductivity and dielectric constant and low viscosity is preferablyused as the organic solvent. However, since the single non-aqueousorganic solvent that satisfies all of the above-described conditions hasnot yet been found, a solvent obtained by mixing together an organicsolvent of a high dielectric constant and an organic solvent of a lowdielectric constant or a solvent obtained by mixing together an organicsolvent of a high dielectric constant and an organic solvent of lowviscosity may be used.

A method of improving the ion conductivity of an organic solventobtained by mixing together a chain carbonate such as dimethyl carbonateor diethyl carbonate and a cyclic carbonate such as ethylene carbonateor propylene carbonate is disclosed in U.S. Pat. Nos. 6,114,070 and6,048,637. However, this organic solvent mixture cannot be used at atemperature higher than 120° C. since a gas may be generated by steampressure at such temperatures such that the battery may swell.

An electrolyte including an organic solvent including at least 20% ofvinylene carbonate (VC) is disclosed in U.S. Pat. Nos. 5,352,548,5,712,059, and 5,714,281. However, since the dielectric constant ofvinylene carbonate is smaller than the dielectric constants of ethylenecarbonate, propylene carbonate and gamma-butyrolactone, when thevinylene carbonate is used as a main solvent, the charge and dischargecharacteristics and the high rate characteristic of the batterysignificantly deteriorate.

On the other hand, in order to suppress the reductive decomposition of asolvent on a negative electrode, a method of adding a compound thatforms a solid electrolyte interface (SEI) on a negative electrode to anelectrolyte as a means of suppressing the reductive decomposition oflithium on the negative electrode is disclosed in Japanese PatentPublication No. hei 2001-6729. However, when such a film formingadditive is used, since a high resistance SEI in which the conductivityof lithium ions is low is formed on the negative electrode, thedischarge characteristic of a battery significantly deteriorates. If anexcessive amount of film forming additive is added to the electrolyte,when the excessive amount of film forming additive is preserved at ahigh temperature, the film forming additive may oxidize and disintegrateon a positive electrode to generate a gas so that the battery maysignificantly swell due to the increase in internal pressure.

SUMMARY OF THE INVENTION

Aspects of the present invention provide an electrolyte for a lithiumsecondary battery that is well preserved at high and low temperaturesand that has a long life.

Aspects of the present invention further provide a lithium secondarybattery including the electrolyte.

According to an aspect of the present invention, there is provided anelectrolyte for a lithium secondary battery including a non-aqueousorganic solvent, lithium salt, and a dicarboxylic acid anhydride and ahalogenated ethylene carbonate as additives.

Also, there is provided a lithium secondary battery including anelectrolyte including a non-aqueous organic solvent, lithium salt, anddicarboxylic acid anhydride and halogenated ethylene carbonate asadditives, a positive electrode including positive electrode activematerials into which lithium ions can be inserted and from which thelithium ions can be separated, and a negative electrode includingnegative electrode active materials into which lithium ions can beinserted and from which the lithium ions can be separated.

Also, there is provided an electrolyte for a lithium secondary batteryincluding a non-aqueous organic solvent, lithium salt, and diglycolicacid anhydride that is substituted or that is not substituted andhalogenated ethylene carbonate as additives. The amount of thediglycolic acid anhydride that is substituted or that is not substitutedis in the range of from 0.1 wt % to 2 wt % based on the weight of thenon-aqueous organic solvent. The amount of the halogenated ethylenecarbonate may be in the range of from 0.1 wt % to 10 wt % based on theweight of the non-aqueous organic solvent.

Also, there is provided a lithium secondary battery including theelectrolyte manufactured according to the embodiment of the presentinvention, a positive electrode including positive electrode activematerials into which lithium ions can be inserted and from which thelithium ions can be separated, and a negative electrode includingnegative electrode active materials into which lithium ions can beinserted and from which the lithium ions can be separated.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a sectional view of a cylinder type lithium secondary battery;

FIGS. 2A and 2B are graphs illustrating room temperature cycle lives oflithium secondary batteries manufactured using electrolytes according toexample 3 of the first embodiment of the present invention andcomparative examples 1, 2, 5, and 6;

FIG. 3 is a graph illustrating high temperature cycle lives of lithiumsecondary batteries manufactured using electrolytes according to example3 of the first embodiment of the present invention and comparativeexample 3;

FIG. 4 is a sectional view of a polygon type lithium secondary battery;

FIG. 5 is a table illustrating room temperature cycle lives of lithiumsecondary batteries manufactured using electrolytes according to example3a of the second embodiment of the present invention and comparativeexamples 1a, 2a, 5a, and 6a; and

FIGS. 6A and 6B are graphs illustrating room temperature cycle lives ofpolygon type lithium secondary batteries manufactured using electrolytesaccording to example 3a of the second embodiment of the presentinvention and comparative examples 1a, 2a, 5a, and 6a.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

An electrolyte according to a first embodiment of the present inventionincludes a dicarboxylic acid anhydride and a halogenated ethylenecarbonate as additives. The electrolyte includes a mixture of thedicarboxylic acid anhydride and the halogenated ethylene carbonate toincrease the life of the battery and to well preserve the battery.

Succinic acid anhydride, maleic acid anhydride, glutaric acid anhydride,itaconic acid anhydride, and mixtures of the above-described anhydridesmay be used as the dicarboxylic acid anhydride. As a specific,non-limiting example, succinic acid anhydride may be used to increasethe life of the battery.

At least one compound of Chemical Formula 1 may be used as thehalogenated ethylene carbonate. As a specific, non-limiting example,fluoroethylene carbonate may be used as the halogenated ethylenecarbonate.

wherein, X represents a halogen atom, Y represents a hydrogen or halogenatom, and n and m represent 1 or 2.

The amount of the dicarboxylic acid anhydride may be in the range offrom 0.1 wt % to 2 wt % based on the weight of the non-aqueous organicsolvent (described later). The amount of the halogenated ethylenecarbonate may be in the range of from 0.1 wt % to 10 wt % based on theweight of the non-aqueous organic solvent. The dicarboxylic acidanhydride and the halogenated ethylene carbonate in the above-describedranges should be mixed with each other to increase the life of thebattery and to well preserve the battery. When only the dicarboxylicacid anhydride is included in the electrolyte, the battery is not wellpreserved at a low temperature. When only the halogenated ethylenecarbonate is included in the electrolyte, the life of the battery isreduced.

It is to be understood that when “a dicarboxylic acid anhydride” and “ahalogenated ethylene carbonate” are mentioned herein, more than onedicarboxylic acid anhydride and/or more than one halogenated ethylenecarbonate can be present. In such a case, the total amount of thedicarboxylic acid anhydrides and the total amount of the halogenatedethylene carbonates should be within the above ranges.

An electrolyte according to a second embodiment of the present inventionincludes a substituted or unsubstituted diglycolic acid anhydride and ahalogenated ethylene carbonate as additives. The diglycolic acidanhydride can be substituted by at least one substituent selected fromthe group consisting of halogen, an alkyl group including from 1 to 10carbon atoms, an alkene group, and an acyl group. The electrolyteincludes a mixture of the diglycolic acid anhydride and the halogenatedethylene carbonate to increase the life of the battery and to wellpreserve the battery.

The amount of the substituted or unsubstituted diglycolic acid anhydridemay be in the range of from 0.1 wt % to 2 wt % based on the weight ofthe non-aqueous organic solvent (described later). The amount of thehalogenated ethylene carbonate may be in the range of from 0.1 wt % to10 wt % based on the weight of the non-aqueous organic solvent. Thebattery can have a long life and can be well preserved when thediglycolic acid anhydride and the halogenated ethylene carbonate in theabove-described ranges are mixed with each other. When only thediglycolic acid anhydride is included in the electrolyte, the battery isnot well preserved at a low temperature. When only the halogenatedethylene carbonate is included in the electrolyte, the life of thebattery is reduced.

The compound of Chemical Formula 1 may be used as the halogenatedethylene carbonate in the electrolyte of the second embodiment. As aspecific, non-limiting example, fluoroethylene carbonate may be used asthe halogenated ethylene carbonate.

It is to be understood that when “a diglycolic acid anhydride” and “ahalogenated ethylene carbonate” are mentioned herein, more than onediglycolic acid anhydride and/or more than one halogenated ethylenecarbonate can be present. In such a case, the total amount of thediglycolic acid anhydrides and the total amount of the halogenatedethylene carbonates should be within the above ranges.

The electrolyte according to either the first embodiment or the secondembodiment includes a non-aqueous organic solvent and lithium salt. Thelithium salt serves as a source of supply of lithium ions in the batteryto enable the lithium battery to basically operate. The non-aqueousorganic solvent serves as a medium through which the ions thatparticipate in the electrochemical reaction of the battery move.

As non-limiting examples, one or a mixture of at least two selected fromthe group consisting of LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiClO₄, LiCF₃SO₃,LiN(SO₂CF₃)₂, LiN(SO₂C2F₅)₂, LiC(SO₂CF₃)₃, LiN(SO₃CF₃)₂, LiC₄F₉SO₃,LiAlO₄, LiAlCl₄, LiCl, and LiI may be used as the lithium salt. Asspecific, non-limiting examples, the concentration of the lithium saltmay be in the range of from 0.6M to 2.0M, and more particularly, may bein the range of from 0.7M to 1.6M. When the concentration of the lithiumsalt is less than 0.6M, the conductivity of the electrolyte is reduced,which deteriorates the performance of the electrolyte. When theconcentration of the lithium salt is greater than 2.0M, the viscosity ofthe electrolyte increases so that the mobility of the lithium ions isreduced.

Carbonate, ester, ether, ketone, and mixtures of the above-describedorganic compounds may be used as the non-aqueous organic solvent. Theorganic solvent should have a large dielectric constant (polarity) andlow viscosity in order to increase the degree of dissociation and theconductivity of ions. As non-limiting examples, at least two mixtures ofa solvent having a high dielectric constant and high viscosity and asolvent having a low dielectric constant and low viscosity may be usedas the organic solvent.

In the non-aqueous organic solvent, as a non-limiting example, a mixtureof a cyclic carbonate and a chain carbonate may be used as acarbonate-based solvent. In this case, as a non-limiting example, thecyclic carbonate and the chain carbonate may be mixed with each other ina volumetric ratio of from 1:1 to 1:9, and more particularly, in avolumetric ratio of from 1:1.5 to 1:4. To obtain a high performanceelectrolyte, the cyclic carbonate and the chain carbonate may be mixedwith each other in the above-described volumetric ratio.

As non-limiting examples, ethylene carbonate (EC), propylene carbonate(PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylenecarbonate, and 2,3-pentylene carbonate may be used as the cycliccarbonate. The dielectric constants of ethylene carbonate and propylenecarbonate are high. As a specific, non-limiting example, ethylenecarbonate may be used as the cyclic carbonate when artificial graphiteis used as a negative electrode active material. As non-limitingexamples, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropylcarbonate (DPC), methylpropyl carbonate (MPC), ethylmethyl carbonate(EMC), and ethylpropyl carbonate (EPC) may be used as the chaincarbonate. Among the above-described carbonates, as specific,non-limiting examples, dimethyl carbonate, ethylmethyl carbonate, anddiethyl carbonate have low viscosity and may be used as the chaincarbonate. Other carbonates may be used.

As non-limiting examples, methyl acetate, ethyl acetate, propyl acetate,methyl propionate, ethyl propionate, γ-butyrolactone, γ-valerolactone,γ-caprolactone, δ-valerolactone, and ϵ-caprolactone may be used as theester. As non-limiting examples, tetrahydrofuran,2-methyltetrahydrofuran, and dibutylether may be used as the ether. As anon-limiting example, polymethylvinyl ketone may be used as the ketone.

An aromatic hydrocarbon-based organic solvent may be further added tothe carbonate-based solvent to obtain the electrolyte. The aromatichydrocarbon-based compound of Chemical Formula 2 may be used as thearomatic hydrocarbon-based organic solvent.

wherein R represents halogen or an alkyl group including from 1 to 10carbon atoms and q represents an integer from 0 to 6.

As non-limiting examples, benzene, fluorobenzene, bromobenzene,chlorobenzene, toluene, xylene, mesitylene, and mixtures of theabove-described organic compounds may be used as the aromatichydrocarbon-based organic solvent. In the electrolyte including thearomatic hydrocarbon-based organic solvent, the carbonate-based solventand the aromatic hydrocarbon-based organic solvent may be mixed witheach other in a volumetric ratio, for example, of from 1:1 to 30:1. Ahigh performance electrolyte can be obtained when the carbonate-basedsolvent and the aromatic hydrocarbon-based organic solvent are mixedwith each other in the above-described volumetric ratio.

The lithium secondary battery including the electrolyte according to thefirst embodiment or the electrolyte according to the second embodimentincludes a positive electrode and a negative electrode.

The positive electrode includes positive electrode active materials intowhich lithium ions can be inserted and from which lithium ions can beseparated. As non-limiting examples, at least one selected from thegroup consisting of Co, Mn, and Ni and at least one selected fromlithium including mixed oxides may be used as the positive electrodeactive materials. As specific, non-limiting examples, the followinglithium compounds may be used.Li_(x)Mn_(1-y)M_(y)A₂  (1)Li_(x)Mn_(1-y)MyO_(2-z)X_(z)  (2)Li_(x)Mn₂O_(4-z)X_(z)  (3)Li_(x)Mn_(2-y)M_(y)M′_(z)A₄  (4)Li_(x)Co_(1-y)M_(y)A₂  (5)Li_(x)Co_(1-y)M_(y)O_(2-z)X_(z)  (6)Li_(x)Ni_(1-y)M_(y)A₂  (7)Li_(x)Ni_(1-y)M_(y)O_(2-z)X_(z)  (8)Li_(x)Ni_(1-y)Co_(y)O_(2-z)X_(z)  (9)Li_(x)Ni_(1-y-z)Co_(y)M_(z)A_(α)  (10)Li_(x)Ni_(1-y-z)Co_(y)M_(z)O_(2-α)X_(α)  (11)Li_(x)Ni_(1-y-z)Mn_(y)M_(z)A_(α)  (12)Li_(x)Ni_(1-y-z)Mn_(y)M_(z)O_(2-α)X_(α)  (13)

wherein, 0.9≤x≤1.1, and 0≤y≤0.5, 0≤z≤0.5, and 0≤α≤2 are equal to eachother or different from each other and are selected from the groupconsisting of Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr,Mn, Cr, Fe, Sr, V, and rare earth elements, A is selected from the groupconsisting of O, F, S, and P, and X is selected from the groupconsisting of F, S, and P.

The negative electrode includes negative electrode active materials intowhich lithium ions can be inserted and from which lithium ions can beseparated. As non-limiting examples, carbon materials such ascrystalline carbon, amorphous carbon, a carbon composite, carbon fiber,a lithium metal, and a lithium alloy may be used as the negativeelectrode active materials. For example, hard carbon, coke, mesocarbonmicrobead (MCMB) annealed at a temperature no more than 1,500° C., andmesophase pitch-based carbon fiber (MPCF) may be used as the amorphouscarbon. Graphite-based materials such as natural graphite, graphitizedcoke, graphitized MCMB, and graphitized MPCF may be used as thecrystalline carbon. As a specific, non-limiting example, a material inwhich an interplanar distance d002 is in the range of from 3.35 Å to3.38 Å and in which a crystallite size Lc caused by X-ray diffraction isno less than 20 nm may be used as the carbon material. As non-limitingexamples, alloys of lithium and Al, Zn, Bi, Cd, Sb, Si, Pb, Sn, Ga, orIn may be used as the lithium alloy.

Electrode active materials, a binder, and a conductive agent and, ifnecessary, a thickener are dispersed into a solvent to obtain anelectrode slurry composition and an electrode collector is coated withthe electrode slurry composition so that the positive electrode or thenegative electrode is manufactured. As non-limiting examples, Al or anAl alloy may be used as a positive electrode collector and Cu or a Cualloy may be used as a negative electrode collector. A foil, a film, asheet, a punched material, a porous material, or a foam may be used asthe positive electrode collector and the negative electrode collector.

The binder converts the active materials into a paste, adheres theactive materials to each other, adheres the active materials to thecollector, and buffers the expansion and contraction of the activematerials. As non-limiting examples, polyvinylidenefluoride, copolymerof polyhexafluoropropylene-polyvinylidenefluoride (P(VdF/HFP)),poly(vinylacetate), polyvinylalcohol, polyethyleneoxide,polyvinylpyrrolidone, alkylated polyethyleneoxide, polyvinylether,poly(methylmethacrylate), poly(ethylacrylate), polytetrafluoroethylene,polyvinylchloride, polyacrylonitrile, polyvinylpyridine,styrene-butadiene rubber, or acrylonitrile-butadiene rubber may be usedas the binder. As non-limiting examples, the amount of the binder may bein the range of from 0.1 wt % to 30 wt % based on the weight of theelectrode active materials, and more particularly, may be in the rangeof from 1 wt % to 10 wt %. When the amount of the binder is too small,the adhesive strength between the electrode active materials and thecollector deteriorates. When the amount of the binder is too large, theadhesive strength between the electrode active materials and thecollector improves, but the amount of the electrode active materials isreduced so that it is disadvantageous to increasing the capacity of thebattery.

The conductive agent improves electronic conductivity and may be formed,for example, of at least one selected from the group consisting of agraphite-based conductive agent, a carbon black-based conductive agent,and a metal-based or metal compound-based conductive agent. Artificialgraphite and natural graphite may be used as the graphite-basedconductive agent. Acetylene black, ketjen black, denka black, thermalblack, and channel black may be used as the carbon black-basedconductive agent. Perovskite materials such as Sn, SnO₂, SnPO₄, TiO₂,KTiO₃, LaSrCoO₃, and LaSrMnO₃ may be used as the metal-based or metalcompound-based conductive agent. However, the conductive agent accordingto the present invention is not limited to the above-describedconductive agents. As a non-limiting example, the amount of theconductive agent may be in the range of from 0.1 wt % to 10 wt % basedon the weight of the electrode active materials. When the amount of theconductive agent is smaller than 0.1 wt %, the electrochemical propertyof the battery deteriorates. When the amount of the conductive agent islarger than 10 wt %, the energy density per weight of the battery isreduced.

Any materials that can control the viscosity of the active materialslurry may be used as the thickener. For example, carboxymethylcellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, andhydroxypropyl cellulose may be used as the thickener.

A non-aqueous solvent or an aqueous solvent may be used as the solventinto which the electrode active materials, the binder, and theconductive agent are dispersed. As non-limiting examples,N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide,N,N-dimethylaminopropylamine, ethyleneoxide, and tetrahydrofuran may beused as the non-aqueous solvent into which the electrode activematerials, the binder, and the conductive agent are dispersed.

The lithium secondary battery may include a separator for preventing thepositive electrode and the negative electrode from being shorted and forproviding a path through which the lithium ions move. As non-limitingexamples, polyolefin-based polymer layers such as polypropylene,polyethylene, polyethylene/polypropylene,polyethylene/polypropylene/polyethylene, andpolypropylene/polyethylene/polypropylene, multi-layers of theabove-described polyolefin-based polymer layers, a fine porous film,fabric cloth, and non-woven fabric may be used as the separator. Also, afilm obtained by coating a porous polyolefin film with a stable resinmay be used as the separator.

FIG. 1 is a sectional view of a cylinder type lithium secondary batterythat can include an electrolyte of the first embodiment or anelectrolyte according to the second embodiment according to aspects ofthe present invention.

Referring to FIG. 1, the cylinder type lithium secondary battery 100includes an electrode assembly 200, a cylinder type can 300 thataccommodates the electrode assembly 200 and an electrolyte, and a capassembly 400 assembled on the top of the cylinder type can 300 to sealup the cylinder type can 300 and to allow the current generated by theelectrode assembly 200 to flow to an external apparatus.

In the electrode assembly 200, a positive electrode plate 210 obtainedby coating the surface of a positive electrode collector with a positiveelectrode coating portion, a negative electrode plate 220 obtained bycoating the surface of a negative electrode collector with a negativeelectrode coating portion, a separator 230 interposed between thepositive electrode plate 210 and the negative electrode plate 220 toelectrically insulate the positive electrode plate 210 and the negativeelectrode plate 220 from each other are wound in the form of ajelly-roll. The positive electrode plate 210 is typically formed of Al.A positive electrode tab 215 that protrudes upward from the electrodeassembly 200 by a predetermined length is connected to one end of thepositive electrode collector. The negative electrode plate 220 includesthe negative electrode collector formed of a conductive metal thin platesuch as a Cu or Ni foil and the negative electrode coating portion withwhich the both surfaces of the negative electrode plate 220 are coated.The negative electrode plate 220 is typically formed of Ni. A negativeelectrode tab 225 that protrudes downward from the electrode assembly200 by a predetermined length is connected to one end of the negativeelectrode collector. The negative electrode tab 225 may also be formedto protrude upward and to thus be connected to the cylinder type can300. Insulation plates 241 and 245 for preventing the electrode assembly200 from being connected to the cap assembly 400 or the cylinder typecan 300 may be further provided on the top and bottom of the electrodeassembly 200.

The cylinder type can 300 includes a cylinder type side plate 310 havinga predetermined diameter so that a predetermined space in which thecylinder type electrode assembly 200 can be accommodated is formed and abottom plate 320 that seals up the bottom of the cylinder type sideplate 310. The top of the cylinder type side plate 310 is opened so thatthe electrode assembly 200 is inserted. The negative electrode tab 225of the electrode assembly 200 is connected to the center of the bottomplate 320 of the cylinder type can 300 so that the cylinder type can 300serves as a negative electrode. A clipping unit 330 curved inward in theupper end thereof to press the top of the cap assembly 400 coupled withthe opening on the top of the cylinder type can 300 is formed in thecylinder type can 300. A beading unit 340 recessed inward to press thebottom of the cap assembly 400 is further formed in the cylinder typecan 300 in the position separated downward from the clipping unit 330 bythe distance corresponding to the thickness of the cap assembly 400. Thecylinder type can 300 is typically formed of Al, Fe, or an alloy of Aland Fe.

The cap assembly 400 includes a safety vent 410, a current interceptingunit 420, a secondary protective element 480, and a cap up or cap cover490.

The safety vent 410 is formed of a conductive metal material in the formof a circular plate that includes a protrusion 412 that protrudesdownward in the center thereof and is positioned in the bottom of thecap assembly 400. The positive electrode tab 215 is electricallyconnected to the bottom of the safety vent 410 and is preferably weldedto the protrusion 412. The protrusion 412 of the safety vent 410 isformed to protrude downward in a normal state and to be reversed upwardwhen the internal pressure of the secondary battery increases due to theexcessive charge and discharge of the secondary battery or the abnormalgeneration of heat by the secondary battery.

In the current intercepting unit 420, a top conductive thin film isformed on the top surface of an insulation printed board and a bottomconductive thin film is formed on the bottom surface of the insulationprinted board. The current intercepting unit 420 includes a via hole 430for connecting the top surface and the bottom surface of the insulationprinted board to each other and a conductive layer 460 formed on theinternal surface of the via hole 430 to electrically connect the topconductive thin film and the bottom conductive thin film to each other.The current intercepting unit 420 is mounted on the safety vent 410 sothat the insulation printed board is broken from the via hole 430 tointercept the current that flows from the safety vent 410 when theprotrusion 412 of the safety vent 410 is reversed.

The secondary protective element 480 in the form of a ring having anexternal diameter corresponding to the external diameter of the safetyvent 410 and a predetermined width is settled on and coupled with thetop of the current intercepting unit 420 to intercept the flow ofcurrent when the temperature of the lithium secondary battery increases.A positive temperature coefficient (PTC) element is preferably used asthe secondary protective element 480.

The cap up or cap cover 490 is settled on and coupled with the top ofthe cap assembly 400 to allow the current generated by the lithiumsecondary battery to flow to the outside.

FIG. 4 is a sectional view of a polygon type lithium secondary batterythat can include either an electrolyte of the first embodiment or anelectrolyte according to the second embodiment according to aspects ofthe present invention.

Referring to FIG. 4, an electrode assembly 12 composed of a positiveelectrode 13, a negative electrode 15, and a separator 14 isaccommodated in a can 10 together with an electrolyte and the top of thecan 10 is sealed up by a cap assembly 20 to form the lithium secondarybattery. The cap assembly 20 includes a cap plate 40, an insulatingplate 50, a terminal plate 60, and an electrode terminal 30. The capassembly 20 is coupled with an insulating case 70 to seal up the can 10.

The electrode terminal 30 is inserted into a terminal through hole 41formed in the center of the cap plate 40. When the electrode terminal 30is inserted into the terminal through hole 41, a tube type gasket 46 iscoupled with the external surface of the electrode terminal 30 in orderto insulate the electrode terminal 30 and the cap plate 40 from eachother so that the tube type gasket 46 is inserted into the terminalthrough hole 41 together with the electrode terminal 30. After the capassembly 20 is assembled with the top of the can 10, the electrolyte isinjected through an electrolyte injection hole 42 and the electrolyteinjection hole 42 is plugged by a plug 43. The electrode terminal 30 isconnected to the negative electrode tab 17 of the negative electrode 15or the positive electrode tab 16 of the positive electrode 13 to serveas a negative terminal or a positive terminal.

The shape of the lithium secondary battery according to aspects of thepresent invention is not limited to the above-described shapes but maybe any shape so long as the lithium secondary battery includes apositive electrode including positive electrode active materials intowhich lithium ions can be inserted and from which the lithium ions canbe separated; a negative electrode including negative electrode activematerials into which lithium ions can be inserted and from which thelithium ions can be separated, and either the electrolyte according tothe first embodiment or the electrolyte according to the secondembodiment.

Hereinafter, examples of the electrolyte according to the firstembodiment of the present invention, along with comparative examples,will be described. However, the following examples are examples only,and the present invention is not limited to the specific examplesprovided.

Example 1

LiCoO₂ as a positive electrode active material, polyvinylidene fluoride(PVdF) as a binder, and carbon as a conductive agent were mixed witheach other in a weight ratio of 92:4:4 and then, the resultant mixturewas dispersed into N-methyl-2-pyrrolidone to manufacture a positiveelectrode slurry. An Al foil having a thickness of 20 μm was coated withthe slurry and then, was dried and rolled to manufacture a positiveelectrode. Artificial graphite as a negative electrode active material,styrene-butadiene rubber as a binder, and carboxymethylcellulose as athickener were mixed with each other in a weight ratio of 96:2:2 andthen, the resultant mixture was dispersed into water to manufacture anegative electrode active material slurry. A Cu foil having a thicknessof 15 μm was coated with the slurry and then, was dried and rolled tomanufacture a negative electrode.

A film separator formed of polyethylene (PE) to have a thickness of 20μm was interposed between the manufactured electrodes and then, theelectrodes with the film separator interposed were wound and compressedto be inserted into a cylinder type can. An electrolyte was injectedinto the cylinder type can to manufacture a lithium secondary battery.LiPF₆ of 1.3M was dissolved in an ethylene carbonate/ethylmethylcarbonate/dimethyl carbonate mixed solvent (in a volumetric ratio of1:1:1) and then, succinic acid anhydride and fluoroethylene carbonatewere added to the resultant solution to manufacture the electrolyte. Atthis time, the amount of the succinic acid anhydride is 0.5 wt % basedon the weight of the organic solvent and the amount of thefluoroethylene carbonate was 1 wt % based on the weight of the organicsolvent.

Example 2

Example 2 is different from example 1 in that the amount of succinicacid anhydride was 0.5 wt % and the amount of fluoroethylene carbonatewas 10 wt %.

Example 3

Example 3 is different from example 1 in that the amount of succinicacid anhydride was 1 wt % and the amount of fluoroethylene carbonate was3 wt %.

Example 4

Example 4 is different from example 1 in that the amount of succinicacid anhydride was 1 wt % and the amount of fluoroethylene carbonate was5 wt %.

Example 5

Example 5 is different from example 1 in that the amount of succinicacid anhydride was 1 wt % and the amount of fluoroethylene carbonate was7 wt %.

Example 6

Example 6 is different from example 1 in that the amount of succinicacid anhydride was 2 wt % and the amount of fluoroethylene carbonate was3 wt %.

Example 7

Example 7 is different from example 1 in that the amount of succinicacid anhydride was 2 wt % and the amount of fluoroethylene carbonate was5 wt %.

Comparative Example 1

Comparative example 1 is different from example 1 in that only succinicacid anhydride, in the amount of 3 wt %, was added.

Comparative Example 2

Comparative example 2 is different from example 1 in that onlyfluoroethylene carbonate, in the amount of 3 wt %, was added.

Comparative Example 3

The comparative example 3 is different from example 1 in that thesuccinic acid anhydride of 0.1 wt % and the fluoroethylene carbonate of15 wt % are added.

Comparative Example 4

Comparative example 4 is different from example 1 in that the amount ofsuccinic acid anhydride was 3 wt % and the amount of fluoroethylenecarbonate was 0.1 wt %.

Comparative Example 5

Comparative example 5 is different from example 1 in that only vinylenecarbonate, in the amount of 3 wt %, was added.

Comparative Example 6

Comparative example 6 is different from example 1 in that vinylenecarbonate in the amount of 1 wt % and fluoroethylene carbonate in theamount of 3 wt % were added.

<Standard Capacity>

Standard capacities when the batteries according to examples 1 to 7 andcomparative examples 1 to 4 were charged under a 0.5 C/4.2V constantcurrent-constant voltage (CC-CV) condition for three hours areillustrated in Table 1.

<Lives at Room Temperature>

The batteries according to examples 1 to 7 and comparative examples 1 to6 were charged at a temperature of 25° C. under a 0.5 C/4.2V CC-CVcondition for three hours, were discharged under a 1 C CC condition, andwere cut off at 3V. After repeating the processes 300 times, thecapacity maintaining ratios (%) in the 300^(th) cycle at the roomtemperature were calculated, and the results are illustrated in Tables 1and 2. Also, graphs of the room temperature cycle lives of the lithiumsecondary batteries according to example 3 and comparative examples 1,2, 5, and 6 are illustrated in FIGS. 2A and 2B.

The capacity maintaining ratio (%) in the 300^(th) cycle=(the dischargecapacity in the 300^(th) cycle)/(the discharge capacity in the firstcycle)*100(%)

<Lives at High Temperature>

The batteries according to example 3 and comparative example 6 werecharged at a temperature of 60° C. under a 0.5 C/4.2V CC-CV conditionfor three hours, wee discharged under a 1 C CC condition, and were cutoff at 3V. After repeating the processes 300 times, the capacitymaintaining ratios (%) in the 300^(th) cycle at the temperature of 60°C. were calculated, and the results are illustrated in Table 2. Also,graphs of the high temperature cycle lives of the lithium secondarybatteries according to example 3 and comparative example 3 areillustrated in FIG. 3.

<Preservation at Low Temperature>

The batteries according to examples 1 to 7 and comparative examples 1 to4 were charged at a temperature of 25° C. under a 0.5 C/4.2V CC-CVcondition for three hours, were preserved at a temperature of 0° C. forfour hours, were discharged under a 0.5 C CC condition, and were cut offat 3V. After preserving the batteries at the low temperature, thedischarge capacity recovery ratios (%) were calculated, and the resultsare illustrated in Table 1.

The discharge capacity recovery ratio (%) after being preserved at thelow temperature=(the 0.5 C discharge capacity after being preserved atthe low temperature)/(the 0.5 C discharge capacity before beingpreserved at the low temperature)*100(%)

<Preservation at High Temperature>

The batteries according to examples 1 to 7 and comparative examples 1 to4 were charged at a temperature of 25° C. under a 0.5 C/4.2V CC-CVcondition for three hours, were preserved at a temperature of 85° C. for24 hours, were discharged under a 0.5 C CC condition, and were cut offat 3V. After preserving the batteries at the high temperature, thedischarge capacity recovery ratios (%) were calculated, and the resultsare illustrated in Table 1.

The discharge capacity recovery ratio (%) after being preserved at thehigh temperature=(the 0.5 C discharge capacity after being preserved atthe high temperature)/(the 0.5 C discharge capacity before beingpreserved at the high temperature)*100(%)

TABLE 1 Discharge Discharge Capacity capacity capacity maintainingrecovery recovery ratio (%) at ratio (%) ratio The The room after (%)after amount amount Standard temperature preservation preservation of SAof FEC capacity in the 300^(th) at 0° C. for 4 at 85° C. for (wt %) (wt%) (%) cycle hours 24 hours Example 1 0.5 1 100 75 96 Example 2 0.5 10100 92 50 93 Example 3 1 3 100 91 73 96 Example 4 1 5 100 91 70 96Example 5 1 7 100 92 68 95 Example 6 2 3 99 91 65 95 Example 7 2 5 99 9264 95 Comparative 3 0 96 71 20 70 example 1 Comparative 0 3 100 49 75 96example 2 Comparative 0.1 15 100 91 40 60 example 3 Comparative 3 0.1 9672 25 96 example 4

TABLE 2 Capacity maintaining The ratio (%) at Capacity The amount Theroom maintaining amount of amount temperature ratio (%) at of SA FEC ofVC in the 300^(th) 60° C. in the (wt %) (wt %) (wt %) cycle 300^(th)cycle Comparative 0 0 3 91 — example 5 Comparative 0 3 1 92 60 example 6Example 3 1 3 0 91 87

SA: succinic acid anhydride, FEC: fluoroethylene carbonate, VC:vinylidene carbonate

As noted from Tables 1 and 2, the electrolytes according to examples 1to 7 that include succinic acid anhydride in the range of from 0.1 wt %to 2 wt % and fluoroethylene carbonate in the range of from 0.1 wt % to10 wt %, based on the weight of the non-aqueous organic solvent, havelong lives and are well preserved. The electrolyte according to thecomparative example 1 that includes only succinic acid anhydride, is notwell preserved at the low temperature. The electrolyte according tocomparative example 2 that includes only the fluoroethylene carbonatedoes not have a long life. The electrolytes according to comparativeexamples 3 and 4 that include excessive amounts of succinic acidanhydride or fluoroethylene carbonate are not well preserved at the lowor high temperature.

The electrolyte according to the comparative example 6 that includesvinylidene carbonate, instead of the succinic acid anhydride, andfluoroethylene carbonate is preserved as well as the electrolyteaccording to the example 3 that includes the succinic acid anhydride andthe fluoroethylene carbonate at room temperature, but is not as wellpreserved at the high temperature.

Hereinafter, examples of the electrolyte according to the secondembodiment of the present invention, along with comparative examples,will be described. However, the following examples are examples only,and the present invention is not limited to the specific examplesprovided.

Example 1a

LiCoO₂ as a positive electrode active material, polyvinylidene fluoride(PVdF) as a binder, and carbon as a conductive agent were mixed witheach other in a weight ratio of 92:4:4 and then, the resultant mixturewas dispersed into N-methyl-2-pyrrolidone to manufacture a positiveelectrode slurry. An Al foil having a thickness of 20 μm was coated withthe slurry and then, was dried and rolled to manufacture a positiveelectrode. Artificial graphite as a negative electrode active material,styrene-butadiene rubber as a binder, and carboxymethylcellulose as athickener were mixed with each other in a weight ratio of 96:2:2 andthen, the resultant mixture was dispersed into water to manufacture anegative electrode active material slurry. A Cu foil having a thicknessof 15 μm was coated with the slurry and then, was dried and rolled tomanufacture a negative electrode.

A film separator formed of polyethylene (PE) to have a thickness of 20μm was interposed between the manufactured electrodes and then, theelectrodes with the film separator interposed were wound and compressedto be inserted into a polygon type can. An electrolyte was injected intothe polygon type can to manufacture a lithium secondary battery. LiPF₆of 1.15M was dissolved in an ethylene carbonate/ethylmethylcarbonate/dimethyl carbonate mixed solvent (in a volumetric ratio of1:1:1) and then, diglycolic acid anhydride and fluoroethylene carbonatewere added to the resultant solution to manufacture the electrolyte. Atthis time, the amount of the diglycolic acid anhydride was 0.5 wt %based on the weight of the organic solvent and the amount of thefluoroethylene carbonate was 1 wt % based on the weight of the organicsolvent.

Example 2a

Example 2a is different from example 1a in that the amount of diglycolicacid anhydride was 0.5 wt % and the amount of fluoroethylene carbonatewas 10 wt %.

Example 3a

Example 3a is different from example 1a in that the amount of diglycolicacid anhydride was 1 wt % and the amount of fluoroethylene carbonate was3 wt %.

Example 4a

Example 4a is different from example 1a in that the amount of diglycolicacid anhydride was 1 wt % and the amount of fluoroethylene carbonate was5 wt %.

Example 5a

Example 5a is different from example 1a in that the amount of diglycolicacid anhydride was 1 wt % and the amount of fluoroethylene carbonate was7 wt %.

Example 6a

Example 6a is different from example 1a in that the amount of diglycolicacid anhydride was 2 wt % and the amount of fluoroethylene carbonate was3 wt %.

Example 7a

Example 7a is different from example 1a in that the amount of diglycolicacid anhydride was 2 wt % and the amount of fluoroethylene carbonate was5 wt %.

Comparative Example 1a

Comparative example 1a is different from example 1a in that onlydiglycolic acid anhydride, in the amount of 3 wt %, was added.

Comparative Example 2a

Comparative example 2a is different from example 1a in that onlyfluoroethylene carbonate, in the amount of 3 wt %, is added.

Comparative Example 3a

Comparative example 3a is different from example 1a in that the amountof diglycolic acid anhydride was 0.1 wt % and the amount offluoroethylene carbonate was 15 wt %.

Comparative Example 4a

Comparative example 4a is different from example 1a in that the amountof diglycolic acid anhydride was 3 wt % and the amount of fluoroethylenecarbonate was 0.1 wt %.

Comparative Example 5a

Comparative example 5a is different from example 1a in that onlyvinylene carbonate, in the amount of 3 wt %, was added.

Comparative Example 6a

Comparative example 6a is different from example 1a in that the vinylenecarbonate, in the amount of 1 wt % and fluoroethylene carbonate, in theamount of 3 wt %, were added.

<Standard Capacity>

Standard capacities when batteries according to examples 1a to 7a andcomparative examples 1a to 4a were charged under a 0.5 C/4.2V constantcurrent-constant voltage (CC-CV) condition for three hours areillustrated in Table 3.

<Lives at Room Temperature>

The batteries according to examples 1a to 7a and comparative examples 1ato 4a were charged at a temperature of 25° C. under a 0.5 C/4.2V CC-CVcondition for three hours, were discharged under a 1 C CC condition, andwere cut off at 3V. After repeating the processes 300 and 500 times, thecapacity maintaining ratios (%) in the 300^(th) and 500^(th) cycles atroom temperature were calculated, and the results are illustrated inTable 3.

Also, the room temperature cycle lives of the lithium secondarybatteries according to example 3a and comparative examples 1a, 2a, 5a,and 6a were measured in the units of ten times to the 500^(th) time, andthe capacity maintaining ratios thereof were calculated. The results areillustrated in FIG. 5. The measured cycle lives and the calculatedcapacity maintaining ratios (%) are illustrated in the graphs of FIGS.6A and 6B.

The capacity maintaining ratio (%) in the nth cycle=(the dischargecapacity in the nth cycle)/(the standard capacity 930 mAh of acell)*100(%)

<Preservation at Low Temperature>

The batteries according to examples 1a to 7a and comparative examples 1ato 4a were charged at a temperature of 25° C. under a 0.5 C/4.2V CC-CVcondition for three hours, were preserved at a temperature of 0° C. forfour hours, were discharged under a 0.5 C CC condition, and were cut offat 3V. After preserving the batteries at a low temperature, thedischarge capacity recovery ratios (%) were calculated, and the resultsare illustrated in Table 3.

The discharge capacity recovery ratio (%) after being preserved at thelow temperature=(the 0.5 C discharge capacity after being preserved atthe low temperature)/(the 0.5 C discharge capacity before beingpreserved at the low temperature)*100(%)

<Preservation at High Temperature>

The batteries according to examples 1a to 7a and comparative examples 1ato 4a were charged at a temperature of 25° C. under a 0.5 C/4.2V CC-CVcondition for three hours, were preserved at a temperature of 85° C. for24 hours, were discharged under a 0.5 C CC condition, and were cut offat 3V. After preserving the batteries at the high temperature, thedischarge capacity recovery ratios (%) were calculated, and the resultsare illustrated in Table 3.

The discharge capacity recovery ratio (%) after being preserved at thehigh temperature=(the 0.5 C discharge capacity after being preserved atthe high temperature)/(the 0.5 C discharge capacity before beingpreserved at the high temperature)*100(%)

TABLE 3 Discharge Discharge Capacity Capacity capacity capacitymaintaining maintaining recovery recovery ratio (%) at ratio (%) atratio (%) ratio (%) The The room room after after amount amount Standardtemperature temperature preservation preservation of DA of FEC capacityin the 300^(th) in the 500^(th) at 0° C. for 4 at 85° C. for (wt %) (wt%) (%) cycle cycle hours 24 hours Example 1a 0.5 1 100 75 55 75 95Example 2a 0.5 10 100 88 82 50 70 Example 3a 1 3 100 86 81 73 95 Example4a 1 5 100 86 81 70 96 Example 5a 1 7 100 87 82 68 94 Example 6a 2 3 9885 81 65 95 Example 7a 2 5 98 85 82 64 95 Comparative 3 0 96 77 50 20 70example 1a Comparative 0 3 100 74 50 75 95 example 2a Comparative 0.1 15100 87 81 40 61 example 3a Comparative 3 0.1 96 78 51 25 95 example 4aDA: diglycolic acid anhydride, FEC: fluoroethylene carbonate

As noted from Table 3 and FIGS. 6A and 6B, the electrolytes according tothe examples 1a to 7a that include diglycolic acid anhydride in therange of from 0.1 wt % to 2 wt % and fluoroethylene carbonate in therange of from 0.1 wt % to 10 wt % based on the weight of the non-aqueousorganic solvent have long lives and are well preserved. The electrolyteaccording to the comparative example 1a that includes only thediglycolic acid anhydride is not well preserved at the low temperature.The electrolyte according to the comparative example 2a that includesonly the fluoroethylene carbonate does not have a long life. Theelectrolytes according to the comparative examples 3a and 4a thatinclude excessive amounts of diglycolic acid anhydride or fluoroethylenecarbonate are not well preserved at the low or high temperature and donot have long lives.

The life at room temperature of the electrolyte that includes vinylidenecarbonate and fluoroethylene carbonate instead of diglycolic acidanhydride according to the comparative example 6a is much shorter thanthe life of the electrolyte that includes the diglycolic acid anhydrideand the fluoroethylene carbonate according to the example 3a.

As described above, the lithium secondary battery including anelectrolyte according to the present invention has a long life and ispreserved well.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

What is claimed is:
 1. A lithium secondary battery comprising: anelectrolyte including a non-aqueous organic solvent, lithium salt, and adicarboxylic acid anhydride and a halogenated ethylene carbonate asadditives, the dicarboxylic acid anhydride being succinic acidanhydride; a positive electrode including positive electrode activematerials into which lithium ions can be inserted and from which thelithium ions can be separated; and a negative electrode includingnegative electrode active materials into which lithium ions can beinserted and from which the lithium ions can be separated, wherein thedicarboxylic acid anhydride is present in an amount of from 0.1 wt % to2 wt % based on the weight of the non-aqueous organic solvent, and thehalogenated ethylene carbonate is present in an amount greater than thatof the dicarboxylic acid anhydride and is present in an amount of from 1wt % to 10 wt % based on the weight of the non-aqueous organic solvent,and wherein the halogenated ethylene carbonate is a compound of ChemicalFormula 1:

wherein X represents a halogen atom, Y represents a hydrogen or halogenatom, and n and m represent 1 or
 2. 2. The lithium secondary battery asclaimed in claim 1, wherein the halogenated ethylene carbonate isfluoroethylene carbonate.
 3. The lithium secondary battery as claimed inclaim 1, wherein the dicarboxylic acid anhydride is present in an amountof from 0.5 wt % to 2 wt % based on the weight of the non-aqueousorganic solvent.
 4. The lithium secondary battery as claimed in claim 1,wherein the positive electrode active materials are lithium compoundsselected from the group consisting of:Li_(x)Mn_(1-y)M_(y)A₂,Li_(x)Mn_(1-y)MyO_(2-z)X_(z),Li_(x)Mn₂O_(4-z)X_(z),Li_(x)Mn_(2-y)M_(y)M_(y)M′_(z)A₄,Li_(x)Co_(1-y)M_(y)A₂,Li_(x)Co_(1-y)M_(y)O_(2-z)X_(z),Li_(x)Ni_(1-y)M_(y)A₂,Li_(x)Ni_(1-y)M_(y)O_(2-z)X_(z),Li_(x)Ni_(1-y)Co_(y)O_(2-z)X_(z),Li_(x)Ni_(1-y-z)Co_(y)M_(z)A_(α),Li_(x)Ni_(1-y-z)Co_(y)M_(z)O_(2-α)X_(α),Li_(x)Ni_(1-y-z)Mn_(y)M_(z)A_(α), andLi_(x)Ni_(1-y-z)Mn_(y)M_(z)O_(2-α)X_(α), wherein, 0.9≤x≤1.1, 0≤y≤0.5,0≤z≤0.5, and 0≤α≤2, M and M′ are equal to each other or different fromeach other and are selected from the group consisting of Mg, Al, Co, K,Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V, and rareearth elements, A is selected from the group consisting of O, F, S, andP, and X is selected from the group consisting of F, S, and P.
 5. Thelithium secondary battery as claimed in claim 1, wherein the negativeelectrode active materials are selected from the group consisting ofcrystalline carbon, amorphous carbon, a carbon composite, carbon fiber,a lithium metal, and a lithium alloy.
 6. The lithium secondary batteryof claim 1, wherein the lithium secondary battery is a cylindrical typeor a polygon type.
 7. An electrolyte for a lithium secondary batterycomprising: a non-aqueous organic solvent; a lithium salt; anddiglycolic acid anhydride and a halogenated ethylene carbonate asadditives, wherein the diglycolic acid anhydride is substituted by atleast one substituent selected from the group consisting of halogen, analkyl group including from 1 to 10 carbon atoms, an alkene group, and anacyl group, wherein the halogenated ethylene carbonate is a compound ofChemical Formula 1:

wherein X represents a halogen atom, Y represents a hydrogen or halogenatom, and n and m represent 1 or
 2. 8. The electrolyte as claimed inclaim 7, wherein the substituted or unsubstituted diglycolic acidanhydride is present in an amount of from 0.1 wt % to 2 wt % based onthe weight of the non-aqueous organic solvent.
 9. The electrolyte asclaimed in claim 7, wherein the halogenated ethylene carbonate ispresent in an amount of from 0.1 wt % to 10 wt % based on the weight ofthe non-aqueous organic solvent.
 10. The electrolyte as claimed in claim7, wherein the halogenated ethylene carbonate is fluoroethylenecarbonate.
 11. The electrolyte as claimed in claim 7, wherein thenon-aqueous organic solvent is at least one selected from the groupconsisting of carbonate, ester, ether, and ketone.
 12. The electrolyteas claimed in claim 11, wherein the carbonate is a mixture of a cycliccarbonate and a chain carbonate.
 13. The electrolyte as claimed in claim12, wherein the cyclic carbonate is at least one selected from the groupconsisting of ethylene carbonate, propylene carbonate, 1,2-butylenecarbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and2,3-pentylene carbonate.
 14. The electrolyte as claimed in claim 12,wherein the chain carbonate is at least one selected from the groupconsisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate,methylpropyl carbonate, ethylmethyl carbonate, and ethylpropylcarbonate.
 15. The electrolyte as claimed in claim 7, wherein thenon-aqueous organic solvent is a mixture of a carbonate-based solventand an aromatic hydrocarbon-based organic solvent.
 16. The electrolyteas claimed in claim 15, wherein the aromatic hydrocarbon-based organicsolvent is an aromatic compound of Chemical Formula 2,

wherein, R represents halogen or an alkyl group including from 1 to 10carbon atoms and q represents an integer from 0 to
 6. 17. Theelectrolyte as claimed in claim 16, wherein the aromatichydrocarbon-based organic solvent is at least one selected from thegroup consisting of benzene, fluorobenzene, chlorobenzene, bromobenzene,toluene, xylene, mesitylene, and mixtures thereof.
 18. The electrolyteas claimed in claim 15, wherein the carbonate-based solvent and thearomatic hydrocarbon-based organic solvent are mixed with each other ina volumetric ratio in the range of from 1:1 to 30:1.
 19. The electrolyteas claimed in claim 7, wherein the lithium salt is at least one or twoselected from the group consisting of LiPF₆, LiBF₄, LiSbF₆, LiAsF₆,LiClO₄, LiCF₃SO₃, LiN(SO₂CF₃)₂, LiN(SO₂C2F₅)₂, LiC(SO₂CF₃)₃,LiN(SO₃CF₃)₂, LiC₄F₉SO₃, LiAlO₄, LiAlCl₄, LiCl, and LiI.
 20. A lithiumsecondary battery comprising: the electrolyte as claimed in claim 7; apositive electrode including positive electrode active materials intowhich lithium ions can be inserted and from which the lithium ions canbe separated; and a negative electrode including negative electrodeactive materials into which lithium ions can be inserted and from whichthe lithium ions can be separated.
 21. The lithium secondary battery ofclaim 20, wherein the lithium secondary battery is a cylindrical type ora polygon type.